Structures conforming to energy codes that require very low air-infiltration of down to 0.5 exchanges per hour within the structure are likely to develop condensation within the walls, resulting in microbial growth, particularly fungal growth. The microbes gain sustenance from the cellulose structural members. Moreover, the proliferation of microbes within the walls may further increase the moisture content. Structural strength can be greatly compromised by such microbial growth and biodegradation of the support members. In addition, the microbes generate metabolic gases and fungi spores that compromise air quality and produce allergens within the living space.
Inorganic boron containing compounds have been used as wood preservatives and fire retardants for many years. The basic compounds are readily available, inexpensive and relatively harmless to humans and their toxicity to fungi, termites, and wood destroying insects has been clearly established. At higher levels of treatment, borates are also effective as fire retardants for lumber and other wood products. For example, U.S. Borax Inc. manufactures a product known as TIM-BOR.RTM. which is a water soluble inorganic borate salt (disodium octaborate tetrahydrate (Na.sub.2 B.sub.8 O.sub.13 .times.4H.sub.2 O)). The product is recommended for use as a 10% or 15% solution or as a foam for control of wood destroying organisms including drywood, dampwood and subterranean termites, wood-boring beetles, carpenter ants, dry-rot fungi and other organisms.
One currently used cellulose fiber based sound and thermal insulation product made from ground after-market cellulose material such as newspaper, cardboard and like cellulose products, is treated with ortho-boric acid (H.sub.3 BO.sub.3) to control biodegradation of the otherwise biodegradable cellulose insulation under temperature and moisture conditions likely to exist within walls of dwelling structures. The boric acid treated cellulose also provides superior fire rating and superior air infiltration control over fiberglass insulation. Unlike fiberglass, boric acid stabilized cellulose is not considered a carcinogen. The insulation is applied, as is fiberglass insulation, within the wall voids, between the studs and in the attic, between and above ceiling joists.
Boric acid will only control pests if the pests contact the acid. Boric acid will also kill fungi upon contact. Boric acid has very low solubility in water, only 4.7% at 20.degree. C., and thus, even if the boric acid treated cellulose becomes wet, the boric acid will not sufficiently leach from the cellulose to penetrate and treat the actual structural members. Boric acid stabilized cellulose as described above thus will treat only those microbes or pests which actually contact the cellulose. In other words, the boric acid will not protect the actual structural members from pests, such as termites and beetles, microbes, such as fungi, or from fire. The boric acid is, in large part, locked out of the structure per se and contributes little or nothing to the fire rating of the actual structural members or to structural pest control.